Preheat oven to 350 degrees. Melt butter in a medium pot over medium heat. Whisk in flour until smooth. Slowly pour in pareve chicken stock, whisking constantly so that mixture thickens. Next slowly add in the half-and-half, whisking constantly so that the mixtures thickens. Stir in the cheese, nutmeg and pepper. Cook for about 2 minutes until cheese is thoroughly incorporated. In a 9 x 13-inch pan place small layer of sauce. Next add a layer of ravioli. Sprinkle cheese over ravioli and cover with sauce. If your family likes spinach, add a layer here. Add another layer of ravioli, more sauce and cover the whole top with cheese. Bake, uncovered, for 45 minutes to 1 hour.